The invention relates to a transfer device for cassettes containing radioactive samples in a gamma counter provided with at least one well-type detector, the transfer device for the cassettes comprising a transfer unit or a path, which is a table provided with at least one conveyor, by which the cassettes of different widths, containing sample containers of different sizes, can be moved one at a time to a lifting position wherefrom the sample containers can be lifted into the measuring unit for measuring.
Gamma counter measurements of radioactive samples are commonly conducted using either RIA (Radio Immuno Assay) devices, then the question usually being of a mass survey, or research devices, the question being of a single research of a small series only. RIA devices must be fast and therefore they handle several samples simultaneously. A research device need not be so fast and samples may, instead, be in containers or cassettes of different sizes. The radioactive isotope of the samples may also emit high energy radiation and therefore the detector of a research device must be larger and the lead shield must be much better than in a RIA device.
Either well-type or diametrically through hole-type detectors are generally used in counters. Well-type detectors are provided with a hollow, formed in the detector material, in which the sample is inserted. In hole-type detectors a hole goes through the detector material into which the sample is lifted. A well-type detector is easier to manufacture. It also has better efficiency and it is easier to shield than a hole-type detector.
Known gamma counters have been disclosed, e.g., in the U.S. Pat. No. 4,029,961 and 4,035,642. In these devices the sample containers to be measured have been placed in cassettes of ten containers and the measuring device takes one cassette at a time for measuring. As there are ten gamma detectors in the device, all samples in the cassette can be measured simultaneously. However, this kind of device is only suitable for use in RIA measurements because it would become too large and expensive for use in research if manufactured using known technique. Moreover, one cannot use a well-type detector in this kind of device because the sample is lifted into the detector.
For economical reasons research devices have only one large and well-shielded detector. Since it has not been possible to combine RIA devices and research devices, those isotope laboratories which want to do both RIA counting and actual gamma research have been forced to purchase two separate counters. Therefore, for economical reasons, counters are also manufactured with 1, 2, or 4 detectors. They are larger and better shielded than necessary in actual RIA work and therefore they can, to a certain extent, be also used in research work. However, the drawback in RIA work is lower speed compared to actual RIA devices and limited efficiency in research work. Furthermore, the volume of samples cannot exceed that of RIA samples.